Dissociation and faceting of asymmetrical tilt grain boundaries: Molecular dynamics simulations of copper

Abstract

Energies and atomic structures of asymmetrical $\ensuremath{\Sigma}11[110]$ tilt grain boundaries in copper have been computed using molecular dynamics with an embedded-atom potential. Two interesting effects have been found: (1) The boundaries dissociate into a low-angle and a high-angle boundary separated by a layer of a fcc-based long-period structure containing intrinsic stacking faults, and (2) the high-energy boundary breaks into nanometer-size facets, some of which are not $\ensuremath{\Sigma}11$ and do not even belong to any coincident-site lattice (CSL). Thus, asymmetrical tilt boundaries locally deviate from the CSL and the average plane imposed by the macroscopic geometry, demonstrating a limitation of the CSL model of grain boundaries. The results are consistent with high-resolution transmission electron microscopy observation available in the literature.